The invention relates to a magnetic device having a monocrystalline, nonmagnetic substrate. The substrate has a surface on which a layer of a monocrystalline, magnetic hexagonal ferrite material is deposited.
Because of their very great uniaxial anisotropies and their small line widths, hexagonal, monocrystalline, thin ferrite layers (e.g. barium-hexaferrite with the simple formula BaO. 6Fe.sub.2 O.sub.3 on nonmagnetic substrates could have exceptional importance. These ferrite layers could, for example, be important as passive microwave components (e.g. as resonance isolators or filters in the centimeter wavelength range), or as components in information storage technology (e.g. in magnetic cylindrical domain devices especially in the field of submicron cylindrical domains). As is already known, magnetic garnet layers, which are used in information storage technology for example, cannot be used at frequencies higher than 50 GHz.
In order to fabricate hexagonal monocrystalline ferrite layers of a quality, homogeneity and crystal perfection as has been achieved, for example, in similar components made with magnetic garnet layers, a monocrystalline substrate is necessary. The substrate must not only have a similar chemical composition as compared to that of the layer grown on it, but it must also have a similar crystallographic structure and an almost identical lattice constant as compared to the layer to be deposited thereon.
Attempts have been made to grow hexagonal monocrystalline ferrite layers, for example with the composition Ba.sub.2 Zn.sub.2 Fe.sub.12 O.sub.22, on hexagonal ferrite substrates with the composition BaFe.sub.12 O.sub.19 by means of liquid phase epitaxy (Mat. Res. Bull. 10 (1975) pp. 1255-1258.) Satisfactory results were not obtained with these substrates according to reports of the work (viz. page 1255, final paragraph, to page 1256, first paragraph).
Attempts were also made to grow hexagonal monocrystalline ferrite layers, for example with the composition Ba0.6Fe.sub.2 O.sub.3, on nonmagnetic spinel substrates with the composition ZnGa.sub.2 O.sub.4 or Mg(In,Ga).sub.2 O.sub.4 by means of epitaxy. These attempts were also unsuccessful; the layers did not grow flawlessly but formed islands on the substrate surfaces to be coated (CF. J. Appl. Phys. 49 (1978) No. 3, pp. 1578-1580.)
For all magnetic applications of the described ferrite layers, the substrate must be nonmagnetic since magnetic substrates adversely affect the magnetic properties of the components to be made with them. Until recently it was not possible to produce monocrystalline hexagonal ferrite layers of good quality, homogeneity and crystal perfection because no suitable substrate was available for seeding.